Ultraviolet sensors have been widely used as an ultraviolet detection device in a germicidal lamp for sterilizing bacteria floating in air or water, an ultraviolet irradiation apparatus or the like, and in recent years, the ultraviolet sensor has also been expected to be applied to an optical communication device.
As this type of ultraviolet sensor, a sensor using a diamond semiconductor or a SiC semiconductor as a sensing material has been known hitherto. However, these diamond semiconductors and SiC semiconductors have defects in that the ability of materials to be processed is inferior and the materials are expensive.
Hence, an oxide semiconductor which is easy in material processing and relatively inexpensive has received attention in recent years, and research on and development of a photodiode type ultraviolet sensor formed by joining a p-type semiconductor layer to an n-type semiconductor layer in the form of a hetero junction by using these oxide semiconductors has been actively pursued.
For example, there is proposed in Patent Document 1, an ultraviolet sensor which includes a (Ni, Zn)O layer composed of an oxide compound semiconductor formed by dissolving ZnO in NiO, a thin film material layer formed so as to cover a part of one main surface of the (Ni, Zn)O layer by sputtering, and a first and a second terminal electrodes formed at both ends of the (Ni, Zn)O layer, and in which an internal electrode is formed in the (Ni, Zn)O layer, the first terminal electrode is electrically connected to the internal electrode and the second terminal electrode is electrically connected to the thin film material layer.
In Patent Document 1, ultraviolet light to be detected does not have to traverse the thin film material layer and reach an upper junction part, and the junction part is directly irradiated with ultraviolet light. Therefore, it is possible to avoid the sensitivity of an ultraviolet sensor from deteriorating by decay of ultraviolet light in transmitting through the thin film material layer. Particularly, when the thin film material layer is made of ZnO, it is possible to obtain an ultraviolet sensor having relatively high wavelength selectivity.